Life histories of Brachycentrus americanus (Banks, 1899) and B. kuwayamai Wiggins et al., 1985 (Trichoptera, Brachycentridae) in Hokkaido, northern Japan

In 2018–2019, life histories of two caddisfly species of the genus Brachycentrus Curtis, B. americanus (Banks, 1899) and B. kuwayamai Wiggins et al., 1985, were studied in Moizari-gawa Creek, Eniwa City (42.8851N, 141.5596E, 35 m above sea level), and in Abira-gawa Creek, Abira Town (42.8746N, 141.9098E, 120 m), respectively, on Hokkaido. Five instars of larvae were detected by head width distribution in both species. Brachycentrus americanus was univoltine with a long adult flight period from mid May–early November. Two larval cohorts were detected in the population, with first instar larvae appearing twice, in July and December. Subsequently, two peaks in the frequency distribution of instars appeared in many months. In contrast, though B. kuwayamai was also univoltine, it had a short adult flight period from late May to mid June, and displayed a narrow range of larval instars in almost all months. In B. kuwayamai, many slender plant pieces (often more than 30 pieces) were attached to about 80% of fourth instar and 95% of fifth instar larval cases. Less than 1% of third to fifth instar B. americanus larvae added 1–4 short plant pieces to their cases. Dominant gut contents of final instar B. americanus larvae were aquatic plant fragments (about 50%) and terrestrial plant fragments (about 30%), and for B. kuwayamai they were amorphous detritus (about 50%) and terrestrial plant fragments (about 25%). The larval frequency feeding on animals increased according to larval development to about 50% in final instar larvae of both species.